Reduktive Ätherspaltung von 6β, 19-Oxido-Δ4-3-ketosteroiden

Summary A report is given of the reductive ether cleavage of 6, 19-oxido-4-androsten-3, 17-dione by zinc amalgam in isopropanol. The general usefulness of this method was demonstrated by the synthesis of 19-hydroxy-4-cholesten-3-one from 6, 19-oxido-4-cholesten-3-one.     

Potassium inactivation in myelinated nerve fibres

Zusammenfassung Die Inaktivierung der K-Permeabilität wurde in Voltage-clamp-Experimenten an markhaltigen Nervenfasern untersucht. Bei langdauernden Depolarisationen fällt der K-Strom annähernd exponentiell auf einen stationären Endwert ab. In Richtung Depolarisation nehmen die Zeitkonstanten dieser Abnahme zu; sie sind um mehrere Grössendornungen grösser als die übrigen Zeitkonstanten. Die Inaktivierungskurve ist s-förmig und bleibt selbst bei grösseren Depolarisationen auf einem endlichen Wert.     

Synaptotagmins I and IV promote transmitter release independently of Ca(2+) binding in the C(2)A domain

At nerve terminals, a focal and transient increase in intracellular Ca(2+) triggers the fusion of neurotransmitter-filled vesicles with the plasma membrane. The most extensively studied candidate for the Ca(2+)-sensing trigger is synaptotagmin I, whose Ca(2+)-dependent interactions with acidic phospholipids and syntaxin have largely been ascribed to its C(2)A domain, although the C(2)B domain also binds Ca(2+) (refs 7, 8). Genetic tests of synaptotagmin I have been equivocal as to whether it is the Ca(2+)-sensing trigger of fusion. Synaptotagmin IV, a related isoform that does not bind Ca(2+) in the C(2)A domain, might be an inhibitor of release. We mutated an essential aspartate of the Ca(2+)-binding site of the synaptotagmin I C(2)A domain and expressed it in Drosophila lacking synaptotagmin I. Here we show that, despite the disruption of the binding site, the Ca(2+)-dependent properties of transmission were not altered. Similarly, we found that synaptotagmin IV could substitute for synaptotagmin I. We conclude that the C(2)A domain of synaptotagmin is not required for Ca(2+)-dependent synaptic transmission, and that synaptotagmin IV promotes rather than inhibits transmission.     

Dantrolene: evidence for effects on Na permeability properties of the nodal membrane

The effects of dantrolene on myelinated frog nerve fibers were studied in voltage clamp experiments. Dantrolene shifted the potential-dependent parameters describing Na+ permeability towards more negative membrane potentials. The findings are interpreted as a change in the negative surface charge of the membrane.     

17β-Hydroxymethyl-Steroide: Darstellung von Derivaten des 17β-Hydroxymethyl-4-androsten-3-ons

Summary Starting from methyl 3-oxo-4-etienate, the authors prepared 17-hydroxymethyl-4-androsten-3-one and 11-hydroxy-17-hydroxymethyl-4-androsten-3-one. Chlorination of 17-acetoxymethyl-4-androsten-3-one yielded 4-chloro-17-acetoxymethyl-4-androsten-3-one. 17-Hydroxymethyl-1, 4-androstadien-3-one was obtained from 17-hydroxymethyl-4-androsten-3-one, both by chemical and biological methods.